1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
As the downsizing of semiconductor devices progresses, it becomes difficult to reliably fill an isolation trench with an insulating film. As a solution to such a problem, there has been proposed a method that utilizes a perhydrosilazane polymer (to be called polysilazane hereinafter). (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-258082.) In this method, a polysilazane solution is applied, and the resultant is subjected to coating, baking, curing and densifying processes, etc., thereby obtaining a silicon oxide film (SiO2 film).
Alternatively, there is a technical idea of using a stack film made of a silicon oxide film formed by a CVD (chemical vapor deposition) method (to be called CVD silicon oxide film), and a silicon oxide film obtained from polysilazane (to be called polysilazane silicon oxide film). However, in this case, the polysilazane film is not sufficiently converted into SiO2 film, and therefore the following problem may occur.
A polysilazane silicon oxide film has an etching rate higher as compared to that of a CVD silicon oxide film. Therefore, when etching a stack film of a polysilazane silicon oxide film and a CVD silicon oxide film in the isolation trench, the etching of the polysilazane silicon oxide film progresses faster and therefore a desired etched form cannot be obtained. Thus, due to such a poor controllability of the etching, the etching amount varies from one place to another depending on the pattern, which creates a problem.
Further, the polysilazane silicon oxide film exhibits a large film contraction in a high-temperature heat process such as the curing or densifying process, and therefore a large stress is created. As a result, the peeling-off of the film easily occurs, which serves as a large factor for lowering the yield.
Furthermore, some of the carbon atoms and nitrogen atoms contained in the polysilazane solution remain in the film, which cause an adverse effect on the properties of the semiconductor device. More specifically, carbon atoms and nitrogen atoms are piled up on the side walls and bottom surface of the isolation trench to create a space charge, thereby significantly varying the shift amount of the field inversion voltage of the transistor (ΔVfb).
As described above, in a stack film made of a CVD silicon oxide film and a polysilazane silicon oxide film, the polysilazane film is not sufficiently converted into SiO2 film, which causes such problems as a poor controllability of the etching, a large stress created in the film and degradation of electrical properties. Therefore, it is conventionally difficult to form an insulating film of excellent properties and reliability.